How to grant download permissions for past woocommerce orders

<?php
/**
 * Plugin Name: Grant download permissions for past WooCommerce orders
 * Plugin URI:  https://github.com/codersmutant/download-permissions-for-past-woocommerce-orders/
 * Description: This plugin grants downloads permissions like WooCommerce 2.6.x, granting permissions for new files added to a downloadable product. 
 * Author:      Coders Mutant
 * Author URI:  https://codersmutant.com/
 * Version:     0.0.3
 * License:     GPLv2 or later
 *
 *
 * @package Grant_Download_Permissions_Like_Legacy_WooCommerce
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit; // Exit if accessed directly.
}

/**
 * WooCommerce_Legacy_Grant_Download_Permissions class.
 */
class WooCommerce_Legacy_Grant_Download_Permissions {

    /**
     * Instance of this class.
     *
     * @var object
     */
    protected static $instance = null;

    /**
     * Initialize the plugin actions.
     */
    private function __construct() {
        // Stop if WooCommerce isn't activated.
        if ( ! class_exists( 'WC_Admin_Post_Types', false ) ) {
            return;
        }

        // Remove WooCommerce 3.0 download permission action.
        remove_action( 'woocommerce_process_product_file_download_paths', array( 'WC_Admin_Post_Types', 'process_product_file_download_paths' ), 10, 3 );

        // Backwards compatibility method.
        add_action( 'woocommerce_process_product_file_download_paths', array( $this, 'grant_download_permissions' ), 10, 3 );
    }

    /**
     * Return an instance of this class.
     *
     * @return object A single instance of this class.
     */
    public static function get_instance() {
        // If the single instance hasn't been set, set it now.
        if ( null === self::$instance ) {
            self::$instance = new self;
        }
        return self::$instance;
    }

    /**
     * Grant download permissions like WooCommerce 2.6.
     *
     * This method performs a heavy query and should not be used for anyone!
     *
     * @param int  $product_id          Product identifier.
     * @param int  $variation_id        Optional product variation identifier.
     * @param array $downloadable_files Newly set files.
     */
    public function grant_download_permissions( $product_id, $variation_id, $downloadable_files ) {
        global $wpdb;

        if ( $variation_id ) {
            $product_id = $variation_id;
        }

        if ( ! $product = wc_get_product( $product_id ) ) {
            return;
        }

        $existing_download_ids = array_keys( (array) $product->get_downloads() );
        $updated_download_ids  = array_keys( (array) $downloadable_files );
        $new_download_ids      = array_filter( array_diff( $updated_download_ids, $existing_download_ids ) );
        $removed_download_ids  = array_filter( array_diff( $existing_download_ids, $updated_download_ids ) );

        if ( ! empty( $new_download_ids ) || ! empty( $removed_download_ids ) ) {
            // Determine whether downloadable file access has been granted via the typical order completion, or via the admin ajax method.
            $existing_orders = $wpdb->get_col( $wpdb->prepare( "SELECT order_id from {$wpdb->prefix}woocommerce_downloadable_product_permissions WHERE product_id = %d GROUP BY order_id", $product_id ) );

            foreach ( $existing_orders as $existing_order_id ) {
                $order = wc_get_order( $existing_order_id );

                if ( $order ) {
                    // Remove permissions.
                    if ( ! empty( $removed_download_ids ) ) {
                        foreach ( $removed_download_ids as $download_id ) {
                            if ( apply_filters( 'woocommerce_process_product_file_download_paths_remove_access_to_old_file', true, $download_id, $product_id, $order ) ) {
                                $wpdb->query( $wpdb->prepare( "DELETE FROM {$wpdb->prefix}woocommerce_downloadable_product_permissions WHERE order_id = %d AND product_id = %d AND download_id = %s", $order->get_id(), $product_id, $download_id ) );
                            }
                        }
                    }

                    // Add permissions.
                    if ( ! empty( $new_download_ids ) ) {
                        foreach ( $new_download_ids as $download_id ) {
                            if ( apply_filters( 'woocommerce_process_product_file_download_paths_grant_access_to_new_file', true, $download_id, $product_id, $order ) ) {
                                // Grant permission if it doesn't already exist.
                                if ( ! $wpdb->get_var( $wpdb->prepare( "SELECT 1=1 FROM {$wpdb->prefix}woocommerce_downloadable_product_permissions WHERE order_id = %d AND product_id = %d AND download_id = %s", $order->get_id(), $product_id, $download_id ) ) ) {
                                    wc_downloadable_file_permission( $download_id, $product_id, $order );
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

add_action( 'admin_init', array( 'WooCommerce_Legacy_Grant_Download_Permissions', 'get_instance' ) );